Multi-layer optical device exhibiting anomalous dispersion

Abstract

An optical device has a first optical layer with a first dispersion response as a first function of wavelength. A second optical layer has a second dispersion response as a function of wavelength that is different than the first function. A separating layer is located between the first and second optical layers and has a lower refractive index than the first layer and the second layer. A thickness of the separating layer is selected such that the first and second dispersion responses combine to create an anomalous dispersion about a target wavelength. The anomalous dispersion results in the optical device emitting a wideband coherent optical output about the target wavelength in response to an optical input at the target wavelength.

The invention claimed is: 
     
       1. An optical device, comprising:
 a first optical layer having a first dispersion response as a first function of wavelength, the first optical layer formed of a first III-V compound; 
 a second optical layer having a second dispersion response as a second function of wavelength different than the first function, the second opticl layer formed of a second III-V compound different from the first III-V compound; and 
 a separating layer between the first and second optical layers having a lower refractive index than the first optical layer and the second optical layer, a thickness of the separating layer selected such that the first and second dispersion responses combine to create an anomalous dispersion about a target wavelength that is between 250 and 500 nm, the anomalous dispersion resulting in the optical device emitting a wideband coherent optical output about the target wavelength in response to an optical input at the target wavelength. 
 
     
     
       2. The optical device of  claim 1 , wherein the first and second optical layers comprise high-index layers having different dispersion curves that are phase matched at the target wavelength to form an avoided-crossing at the target wavelength. 
     
     
       3. The optical device of  claim 1 , wherein a thickness of the separating layer controls a coherent coupling between the first and second optical layers, adjusts a curvature of anti-crossing, and a bandwidth of the anomalous dispersion in a heterostructure. 
     
     
       4. The optical device of  claim 1 , wherein the first and second optical layers are configured such that anti-crossing behavior of first and second dispersion curves results in a supermode of the optical device such that the anomalous dispersion about the target wavelength exceeds a normal material dispersion of the optical device about the target wavelength. 
     
     
       5. The optical device of  claim 1 , wherein the first and second optical layers are phase matched at the target wavelength and phase mismatched away from the target wavelength. 
     
     
       6. The optical device of  claim 1 , wherein the wideband coherent optical output comprises a quasi-transverse electric (TE) polarization. 
     
     
       7. The optical device of  claim 1 , wherein the wideband coherent optical output comprises a bright-soliton frequency comb. 
     
     
       8. The optical device of  claim 1 , wherein the optical device comprises a ring resonator that comprises the first and second optical layers and the separating layer, and wherein the optical input comprises a continuous wave laser. 
     
     
       9. The optical device of  claim 1 , wherein the optical device comprises a waveguide that is driven by an optical pulsed laser. 
     
     
       10. The optical device of  claim 1 , wherein the first and second optical layers are formed on a substrate made out of silicon, sapphire, GaAs, or SiC. 
     
     
       11. The optical device of  claim 1 , wherein the separating layer comprises at least one of AlGaN, AlGaInN, GaN, Al 2 O 3 , SiC, SiON, Si 3 N 4 , HfO 2 , Ta 2 O 5 , TiO 2 , TiN or SiO 2 , as selected to achieve required dispersive properties. 
     
     
       12. The optical device of  claim 1 , wherein the optical device has tapered sides extending along a light propagation direction of the optical device. 
     
     
       13. An optical device, comprising:
 a first optical layer having a first dispersion response as a first function of wavelength, wherein the first optical layer comprises Al x1 Ga 1−x1-y1 In y1 N; 
 a second optical layer having a second dispersion response as a second function of wavelength different than the first function, wherein the second optical layer comprises Al x2 Ga 1−x2-y2 In y2 N, wherein x 1 ≠x 2  or y 1 ≠y 2 ; and 
 a separating layer between the first and second optical layers having a lower refractive index than the first optical layer and the second optical layer, a thickness of the separating layer selected such that the first and second dispersion responses combine to create an anomalous dispersion about a target wavelength, the anomalous dispersion resulting in the optical device emitting a wideband coherent optical output about the target wavelength in response to an optical input at the target wavelength. 
 
     
     
       14. The optical device of  claim 13 , wherein the separating layer comprises a III-Nitride film. 
     
     
       15. The optical device of  claim 13 , wherein the first and second optical layers are formed on a single crystalline AlN layer. 
     
     
       16. A method comprising:
 selecting first and second different III-V compounds for first and second optical layers of an optical device, the first and second different III-V compounds having different dispersion responses as a function of wavelength; 
 forming the first and second optical layers with a separating layer therebetween, the separating layer having a lower refractive index than the first and second optical layers, the first and second optical layers having a geometry that, together with the first and second III-V compounds, result in the first and second optical layers and the separating layer forming a heterostructure of the optical device with an anomalous dispersion about a target wavelength, the target wavelength being in a visible to UV spectrum; and 
 coupling an optical input into the heterostructure, the optical input comprising an optical continuous-wave laser at the target wavelength, the anomalous dispersion of the heterostructure resulting in emission of a wideband coherent optical output signal about the target wavelength in response to the optical input. 
 
     
     
       17. The method of  claim 16 , wherein the wideband coherent optical output signal comprises optical information at a speed greater than 1 GHz. 
     
     
       18. The method of  claim 16 , wherein the wideband coherent optical output signal comprises a bright-soliton frequency comb.